如何修复 stream 错误：可能无法关闭 stream 错误

Question

I am writing a method but see this error: may fail to close stream. According to some solutions on different posts, I have added try and catch within the finally block. I also added IOUtils.closeQuietly(fullObject, (Log) LOGGER). But it still doesn't work. Anyone can help take a look? Thanks!

        S3Object fullObject = null;
        StringBuffer buffer = new StringBuffer();

        try {
            S3Object s3Response = s3Client.getObject(s3BucketName, s3Key);
            BufferedReader reader = new BufferedReader(new InputStreamReader(s3Response.getObjectContent()));
            String line;
            while ((line = reader.readLine()) != null) {
                buffer.append(line);
            }
        } finally {
                if (fullObject != null) {
                    try {
                        fullObject.close();
                    } catch (IOException ex) {
                        throw new RuntimeException(ex);
                    }
                    IOUtils.closeQuietly(fullObject, (Log) LOGGER);
                }
        }
        return buffer.toString();
    }

Answer 1

InputStreamReader implements AutoCloseable . This means that the intended use is try-with-resources :

try (InputStreamReader reader = new InputStreamReader(s3Response.getObjectContent()) {
    ...
}

This should always close the stream irrespective of how the block exits (ie through normal completion, catch or finally clauses).

The same is true for S3Object and BufferedReader . They can all be declared as resources within the same try block.

See https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html for more details.

Answer 2

You should be using Java 7+ try with resources . It will take care of closing the resources you declare in the list. Any exceptions that may be thrown in the process of closing will be dealt with appropriately. (They are either allowed to propagate, or they are "suppressed" if an exception was already propagating.)

Your code using try with resources would look like this. It is half the length of the original version AND it won't have any resource leaks. You "win" both ways.

try (S3Object s3Response = s3Client.getObject(s3BucketName, s3Key);
     BufferedReader reader = new BufferedReader(
             new InputStreamReader(s3Response.getObjectContent()));
    ) 
{
    StringBuffer buffer = new StringBuffer();
    String line;
    while ((line = reader.readLine()) != null) {
        buffer.append(line);
    }
    return buffer.toString();
}

Notice that I have gotten rid of fullObject which your code wasn't using.

There are actually two managed resources in the above: the s3Response and the reader . It might not be strictly necessary to close both, but (IMO) closing them anyway is the correct thing to do... from the perspective of readability, if nothing else.

^{(It may also be possible to do the "read content as a string" more simply and/or more efficiently, but that is outside of the scope of this question.)}